When solid sodium hydroxide is dissolved in water the temperature of the solution rises. This dissolution is therefore a/an:

1. A rise in temperature means heat is being given out to the surroundings. 2. A process that gives out heat is exothermic, so dissolving NaOH is exothermic. 3. If heat were absorbed the temperature would fall, which would be endothermic. 4. Dissolution is not a chemical reaction here; no new substance forms, so the decomposition and displacement options do not apply. _Source: Balbharati (Maharashtra Board) Class 10 Science & Technology, Ch 3 "Chemical Reactions and Equations", p.48_